Response of strawberry quality and profitability to farmyard manure and triple super phosphate under tropical high altitude conditions

Quality of strawberries in the tropics is partly limited by poor soil fertility, while profitability of different nutrient management strategies has not been established. The present study determined the effect of 0, 18, 36, and 54 t/ha farmyard manure (FYM) and triple super phosphate (TSP), equivalent to 0, 17, 34 and 68 kg/ha phosphorus (P) on quality and profitability of strawberries. The study was done in three seasons on field 3 of Tatton farm-Njoro, Kenya. The design was split-plots embedded in  randomised complete blocks, replicated three times. The FYM and TSP were broadcasted to main plots and sub-plots, respectively. Each treatment had 10 plants, spaced at 0.3 m x 0.45 m in 0.6 m x 1.5 m plots, mulched with black polyfilm and irrigated with drip lines. Berry fruit size, brix index and storage life were determined from 26 to 42 weeks after planting (WAP). Profitability was calculated using berry yield-income and input-costs at the end of the study. Results varied depending on response variable. High FYM and TSP significantly (P < 0.05) increased fruit size, but lowered storage life. High FYM significantly lowered brix index. Low FYM  plus moderate P significantly lowered fruit size. Thus, 54 t/ha FYM plus 34 kg/ha P and 36 t/ha FYM plus 17 kg/ha P are recommended for  large-sized and sweetest, long-storing berries, respectively. Manure alone increased profitability more than TSP alone. Highest FYM and TSP did not always result in highest profitability. The relationship between treatments and profitability was sigmoid, and dependent on site and season. Thus, profitable strawberry mineral nutrition packages will have to be developed for each site and season in Kenya. &nbsp

Explants, hormones and sucrose influence in vitro shoot regeneration and rooting of calla lily (Zantedeschia albomaculata L. Spreng.) ‘black magic'

Zantedeschia is an important and rapidly expanding cut flower in Kenya today. A protocol for in vitro shoot regeneration of Zantedeschia, using tuber, leaf and shoot primordium explants on Murashige and Skoog (MS) (1962) basal salts, supplemented with 6-benzyalamino purine (BAP) or Kinetin is described. Of the four levels (0, 1, 2, and 4 mg/l) each of BAP and Kinetin, 2 mg/l BAP induced the highest number of shoots per explant (2.5) and the longest shoots (3.7 cm) on shoot explants after four weeks in culture. No response was observed on both leaf and tuber explants on all media tested. A 34-fold shoot multiplication rate was achieved in a culture period of 10 weeks. Rooting was tested using three levels (0, 1, and 2 mg/l) each of naphthalene acetic acid (NAA) and indole butyric acid (IBA) in combination with three levels (15, 20 and 30 g/l) of sucrose. The highest (84%) root induction in the shortest time (within one week) occurred in the medium containing 20 g/l sucrose + 1 mg/l IBA. However after four weeks, all shoots (100%) in this medium and the hormone-free media plus 15 to 30 g/l sucrose had rooted. Thus, this research established that shoot explants of Zantedeschia albomaculata cultivar Black Magic can be induced to produce high quality multiple shoots, using MS (1962) basal salts, supplemented with 2 mg/l BAP, 30 g/l sucrose and 0.8% agar. All the shoots can be readily and inexpensively rooted in growth regulator-free medium, containing 15 to 30 g/l sucrose, before transferring plantlets ex vitro. Journal of Agriculture, Science and Technology Vol. 7(1) 2005: 53-6

Elucidating the molecular responses of apple rootstock resistant to ARD pathogens: challenges and opportunities for development of genomics-assisted breeding tools

Apple replant disease (ARD) is a major limitation to the establishment of economically viable orchards on replant sites due to the buildup and long-term survival of pathogen inoculum. Several soilborne necrotrophic fungi and oomycetes are primarily responsible for ARD, and symptoms range from serious inhibition of growth to the death of young trees. Chemical fumigation has been the primary method used for control of ARD, and manipulating soil microbial ecology to reduce pathogen density and aggressiveness is being investigated. To date, innate resistance of apple rootstocks as a means to control this disease has not been carefully explored, partly due to the complex etiology and the difficulty in phenotyping the disease resistance. Molecular defense responses of plant roots to soilborne necrotrophic pathogens are largely elusive, although considerable progress has been achieved using foliar disease systems. Plant defense responses to necrotrophic pathogens consist of several interacting modules and operate as a network. Upon pathogen detection by plants, cellular signals such as the oscillation of Ca(2+) concentration, reactive oxygen species (ROS) burst and protein kinase activity, lead to plant hormone biosynthesis and signaling. Jasmonic acid (JA) and ethylene (ET) are known to be fundamental to the induction and regulation of defense mechanisms toward invading necrotrophic pathogens. Complicated hormone crosstalk modulates the fine-tuning of transcriptional reprogramming and metabolic redirection, resulting in production of antimicrobial metabolites, enzyme inhibitors and cell wall refortification to restrict further pathogenesis. Transcriptome profiling of apple roots in response to inoculation with Pythium ultimum demonstrated that there is a high degree of conservation regarding the molecular framework of defense responses compared with those observed with foliar tissues. It is conceivable that the timing and intensity of genotype-specific defense responses may lead to different outcomes between rootstocks in response to invasion by necrotrophic pathogens. Elucidation of host defense mechanisms is critical in developing molecular tools for genomics-assisted breeding of resistant apple rootstocks. Due to their perennial nature, use of resistant rootstocks as a component for disease management might offer a durable and cost-effective benefit to tree performance than the standard practice of soil fumigation for control of ARD